Many structures have pitched, shingled roofs, which prevent water, e.g., rain water, from entering the structures by causing water to pass over the shingles and off the roofs. A pitched, shingled roof has a pitched substrate, such as a plurality of plywood sheets, with a plurality of shingles attached thereto.
Each shingle has an upper portion (i.e., a headlap portion) and a lower portion (i.e., an exposure portion) wherein the exposure portion is exposed to the environment. The shingles are typically attached to the substrate in rows known as courses wherein the exposure portion of an upper course of shingles overlaps the headlap portion of an adjacent lower course of shingles. For example, a first course of shingles may be attached to the substrate nearest the lowest point of the roof, i.e., the eave portion of the roof. A second course of shingles may then be attached to the substrate slightly higher on the roof than the first course. The shingles are placed so that the exposure portion of the second course of shingles overlaps the headlap portion of the first course of shingles. This overlapping continues with successive rows of shingles to the highest point on the roof, i.e., the hip or the ridge. Thus, only the exposure portion of the shingles are exposed to the environment. This overlapping of the shingles causes water to pass from shingles on a high course to shingles on the next lowest course of shingles without contacting the substrate. Accordingly, water passes from shingle to shingle and off the roof without contacting the substrate or entering the structure.
Attaching the shingles to the roof is typically achieved by the use of nails or other fastening devices that pass through the shingles and into or through the substrate. The fastening devices are typically placed through the headlap portion of the shingles so that they are overlapped by shingles in an adjacent higher course as described above. This placement of the fasteners prevents water from entering the structure through holes caused by the fasteners.
Some roofs have a membrane (i.e., an underlayment) located between the substrate and the shingles. The membrane may, as an example, be conventional tar paper that is nailed to the substrate. Strips of the membrane are typically attached to the roof in an overlapping fashion wherein an upper strip overlaps its adjacent lower strip. Accordingly, the membrane serves to shield the substrate from water should a shingle become damaged. For example, if a shingle becomes cracked or otherwise leaks, water will contact the membrane rather than the substrate. Water will then pass along the membrane to the next lowest shingle without contacting the substrate or entering the structure. Alternatively, water will pass along the membrane, under the shingles and off the roof.
Shingles may be damaged by impacts from hail or debris in a storm, or by prolonged exposure to the elements and temperature cycles. Existing methods of reroofing a shingled roof involve removing the shingles, fasteners, and membrane before applying new membrane and shingles.